1. Field of the Invention
The present invention relates to the fabrication of structural members such as trusses, particularly for use in space. The usefulness of large orbiting space structures such as solar energy collecting stations and various other types of space stations is now widely recognized. In constructing such structures, it is impracticable to transport the building materials to the space construction site in the form of completed structural units such as trusses. Only relatively few such units could be transported in a single trip of the space shuttle or other vehicle. Thus the cost of transporting enough units to construct a large space structure would be prohibitive.
It is thus extremely important that techniques be developed for forming the structural units in space and that the construction materials be transported into space in the most compact form possible. At the same time it is necessary that these materials be as lightweight as possible and that the amount of material needed to construct a given item be minimized.
It thus becomes readily apparent that conventional construction materials, such as dense, rigid metal beams, plates, and the like are not practical for use in such projects. However, the environment of space with its low gravitational forces and relative freedom from airborne chemicals of various kinds permits the use of unique construction materials which would be unsuitable for like use on earth.
The use of such different materials, along with the differences in the space environment, in turn make the construction techniques conventionally used on earth impractical for use in space, and drastically different methods are indicated. Among the requirements of such different methods are that the fabrication process be as fully automated as possible and that the amount of additional material needed to fasten various component elements together be minimized.
2. Description of the Prior Art
U.S. Pat. Nos. 3,961,738 and 3,840,960 each disclose somewhat automated devices for manufacturing structural units. However, neither the raw materials, the manufacturing devices, nor the finished products as well suited for use in space. The raw materials include metal of substantial density and inherent rigidity, and the manufacturing methods and devices are adapted to these materials rather than to the types which are preferably used to form structural members for use in space. The finished products are likewise heavier than is proper for space structures. The techniques disclosed also involve numerous other features which would be undesirable for space use. For example, the device of U.S. Pat. No. 3,961,738 requires a separate connecting medium, namely a welding material, which constitutes additional weight and takes up additional space.
U.S. Pat. Nos. 3,740,812, 3,768,130, and 2,141,642 also disclose techniques for forming structural units which make some attempt to minimize the number of separate parts which must be attached together. However, again each of the prior patents is unsuitable for space use because of the rigidity and/or weight of the initial materials and/or the need for separate connecting elements or media.
U.S. Pat. Nos. 2,316,349 and 3,940,962 suggest means for forming cylindrical members from sheet material. The latter of these two patents also suggests means for fastening metal without additional connecting means, as do U.S. Pat. Nos. 3,722,280 and 3,470,596. However, none of these prior patents disclose apparatus which is well suited for use in space, nor are they suggestive of a total scheme for forming a structural member such as a truss.